Iron in infants

My 4 month old is a little pale, slightly lagging behind in head/neck control, low percentile for weight. I was anemic at the end of 3rd trimester, and now, despite taking iron supplements. I almost exclusively pump, adding 3-4 oz formula per day.

My lactation consultant says baby might be iron deficient, because there might not be enough iron in my breast milk. My pediatrician on the other hand says there is no iron intake from milk before solids are introduced, babies survive on iron stored during pregnancy.

We are going to do blood work, of course, but who is right?